Hafnium Hydride Control Rod for Light Water Reactors
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Solution Overview
Problem
In light water reactors, control rods made of hafnium can experience dimensional changes and helium gas formation, leading to structural issues and increased risk of cracks and bending, while boron carbide absorbers can cause swelling and damage.
Innovation Solution
A control rod with at least 90% of its absorber material in the form of hafnium hydride, which reduces hydrogen pickup and helium gas formation, and includes a cubic lattice structure for stability, with a stoichiometric equilibrium ratio of hafnium to hydrogen (1.40 ≤ x ≤ 1.80) to maintain dimensional stability and prevent gas emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hafnium is used as absorber material in light water reactors, then good neutron absorption capacity is achieved, but dimensional changes occur due to hydrogen pickup leading to cracks and bending
Solution Approach 1:
The control rod is pre-hydrogenated during manufacturing to achieve a predetermined hydrogen content (0.5-5 wt%). This preliminary action saturates the hafnium's hydrogen absorption capacity before reactor operation, preventing further hydrogen pickup and associated dimensional changes during service. The pre-established hydrogen content creates a buffer that eliminates future dimensional instability.
Solution Approach 2:
The invention changes the hydrogen content parameter of the hafnium absorber material from its initial state (0% or low) to a controlled range (0.5-5 wt%). By adjusting this chemical composition parameter during manufacturing, the material's dimensional stability is improved while maintaining its neutron absorption properties. This parameter change transforms the material's behavior during reactor operation.
2Reliability
If boron carbide is used as absorber material, then neutron absorption is achieved, but helium gas formation causes swelling and damage to surrounding materials
Solution Approach 1:
The invention replaces boron carbide (which generates harmful helium gas) with hafnium hydride. The hydrogen in hafnium hydride acts as a beneficial substitute that prevents helium formation. When neutrons interact with hafnium hydride, hydrogen is released as a harmless gas instead of helium, converting a potentially harmful situation into a beneficial one. The hafnium hydride thus serves dual purposes: maintaining neutron absorption while eliminating helium gas generation.
3Reliability
If control rods are designed with water channels for moderation, then neutron moderation is improved, but structural complexity and potential for dimensional instability increase
Solution Approach 1:
The hafnium hydride absorber material performs multiple functions simultaneously: it provides neutron absorption through hafnium and neutron moderation through the hydrogen content. This multi-functionality eliminates the need for separate water channels that would otherwise be required for moderation. The absorber material itself becomes the moderator, simplifying the overall control rod structure while maintaining both absorption and moderation capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of hafnium hydride as the primary absorber material in control rods reduces the risk of dimensional changes, helium gas formation, and structural instability, while providing improved neutron absorption and mechanical stability, thus enhancing the operational safety and efficiency of light water reactors.
Implementation Method 1
hafnium has a good absorption capacity for thermal neutrons
Implementation Method 2
the hafnium may pick up hydrogen during use in the light water reactor, i.e. the hafnium is hydrogenated
Data Source
Figure 1~2
AI summary
The invention concerns a control rod configured for a nuclear power light water reactor of the BWR or PWR kind. The control rod contains absorber material. At least 50%, with respect to weight, of the absorber material that is in the control rod is in the form of hafnium hydride. The invention also concerns the use of such a control rod during operation in a nuclear power light water reactor of the BWR or PWR kind.